2,3-Butanediol (BDO) is a useful compound having 3 types of optical isomers, and is used as an intermediate material for pharmaceuticals and cosmetics; and as a material for inks, perfumes, liquid crystals, insecticides, softening agents, explosives, plasticizers and the like. Industrially, it is produced by a method in which 2-butene oxide is hydrolyzed in an aqueous perchloric acid solution. On the other hand, in recent years, to solve the problems of depletion of petroleum resources and global warming, achievement of a sustainable, recycling-oriented society is demanded. Also, in the chemical industry, shifting from petroleum materials to biomass-derived materials is being intensively studied. In particular, microbial fermentation of 2,3-butanediol is attracting attention. It has been reported that 2,3-butanediol is converted to methyl ethyl ketone, which is a general-purpose solvent, by chemical conversion (A. N. Bourns, The Catalytic Action of Aluminium Silicates, Canadian J. Res. (1947)), and that 2,3-butanediol is converted to 1,3-butadiene by acetylation followed by elimination of acetic acid (Nathan Shlechter, Pyrolysis of 2,3-butylene Glycol Diacetate to Butadiene, Indu. Eng. Chem. 905 (1945)). In particular, production techniques for 1,3-butadiene are very important since 1,3-butadiene is a starting substance that enables synthesis of many kinds of compounds such as hexamethylenediamine, adipic acid and 1,4-butanediol, and establishment of those techniques might replace the existing petroleum-derived synthetic resins with biomass-derived resins.
Examples of generally known microorganisms that produce 2,3-butanediol include Klebsiella Pneumoniae, Klebsiella axytoca and Paenibacillus polymyxa, and 2,3-butanediol is produced by fermentation production by these microorganisms. However, fermentation liquids contain not only 2,3-butanediol, but also various impurities such as residual medium components and metabolic by-products of the microorganisms. In particular, sugars as nutrient sources for the microorganisms; organic acids and proteins as their metabolic products and the like are reported to generate colored impurities by heat (Yoshiyuki Matsuo, Mode of Overdecomposition of Glucose by Acid: Journal of Fermentation Technology 39, 5, 256-262 (1961)). Therefore, application of the fermentation liquid to the above-described uses require high-level purification of 2,3-butanediol.
As a method of purifying 2,3-butanediol, JP 2010-150248 A discloses a purification method in which a diol such as 2,3-butanediol is purified by combination of nanofiltration membrane treatment and distillation. As another method for purifying a diol, U.S. Pat. No. 6,361,983 B discloses a method in which the pH of a 1,3-propanediol fermentation liquid is adjusted to not less than 7 and the resulting fermentation liquid is then subjected to a separation step, to reduce coloration of 1,3-propanediol. As a method of producing a highly pure diol, Japanese Translated PCT Patent Application Laid-open No. 2007-502325 discloses a method of producing 1,3-propanediol by microfiltration, ultrafiltration, nanofiltration, ion exchange, distillation and then hydrogenation reduction treatment.
In the above-described method of purifying 2,3-butanediol, that is, in the purification of a 2,3-butanediol fermentation liquid by nanofiltration membrane treatment followed by distillation, highly pure 2,3-butanediol can be obtained, but there still remains a problem that the distillation step causes remarkable coloration of the 2,3-butanediol. In view of this, it could be helpful to provide a method of purifying a 2,3-butanediol fermentation liquid by distillation, wherein 2,3-butanediol is separated/recovered while coloration of 2,3-butanediol is prevented.